120 



MOLLUSCA. 



[Sessilia. 



Found on the Northumberland coast, near Seaton. In Lady 

 Jardine's cabinet. 



5. Pentelasmis radula, pi. LI, f. 3. 



Anatifa radula, First Ed., pi. 5, f . 3 ; Pentelasmis radula, 

 Leach, MSS.; Lepas dentata, Brown, Ency. Brit., VI, p. 404. 



Shell subcompressed ; the larger valves acutely pointed, with 

 regular scries of prominent, oblique ribs, their anterior edges 

 with six sharp, saw-like teeth, the superior ones largest, and 

 gradually diminishing as they descend, thickly beset with sharp, 

 imbricated scales, which have a rasp-like appearance ; superior 

 valves terminating in a lengthened, acute point, and covered by 

 undulating, rough stria;; dorsal valve arcuated, and smooth; 

 peduncle very small. 



Besides the ribs on the larger valves, the series of teeth on 

 the anterior margins of the larger valves will at once distinguish 

 this curious species from P. dentatus, in which the serrated 

 teeth are placed on the centre of the dorsal valve. 



Found on the Devonshire coast, but is very rare. 



6. Pentelasmis fascicularia, pi. LI, f. 2. 



Anatifa fascicularia, First Ed., pi. 5, f. 2 ; Pentalasmis 

 Ellisii, Leach, MSS., p. 1 ; Anatifa vitrea, Lamarck, V, p. 

 405 ; Ellis, Zoophytes, p. 167, pi. 15, f. 6 ; Lepas fascicularis, 

 Montagu, p. 557 ; Maton and Kackett, p. 30 ; Lepas dilata, 

 Donovan, pi. 144. 



Shell of a pale horn-colour, extremely thin and fragile ; valves 

 with large wrinkles ; larger valves much expanded posteriorly, 

 and becoming suddenly hollow, terminate in a beak-like point ; 

 dorsal valve with an acute protuberance in its centre, aud fre- 

 quently with one below ; apicial valves much pointed, and have 

 a considerable inclination backwards, producing a convexity on 

 the anterior side of the shell ; peduncle very short, and very 

 thin. 



This species is always found congregating in large masses. 



First found in the British Channel, and has been since met 

 with on many of the British coasts, and especially on the west- 

 ern coast of Ireland. 



ORDER II— SESSILIA. 



Genus 1. — Pybgoma — Savigny. 



Shell univalve, somewhat conical, generally compressed, and 

 usually seated on Madrepores or other zoophytes ; open at the 

 apex, which is small, and protected by a four-valved operculum, 

 the posterior ones sometimes much elongated, these are varia- 

 ble, and closed at the base by a deeply cup-shaped testaceous 

 valve ; inside perpendicularly striated or grooved. 



1. Pyrgoma Anglica, pi. LIII, f. 27, 28, 29. 



Adna Anglica, First Ed., pi. 7, f. 27, 28, 29; Leach, MSS., 

 p. 1. 



Shell conical, longitudinally ribbed, with many, nearly obso- 

 lete, transverse wrinkles ; apex with a very small aperture, and 

 protected by a bivalve, obliquely striated operculum ; colour 

 rosy. 



Fig. 28, the operculum. 



Inhabits the Curt/ophil/ia Anglica, and is frequently found 

 in Plymouth Sound. 



Genus 2 — Balanus. — Bruguiere. 



Shell sessile, conical ; frequently an elongated cone ; com- 

 posed of six valves, four of which are larger than the others, 

 and of nearly equal size, and all of them locked by their 

 sides ; apex open, of a subtrigonal or elliptical form ; base 

 closed by a testaceous plate, by which it adheres to extra- 

 neous substances ; operculum bipartite, and consisting of four 

 valves, of which the posterior pair are the most prominent ; 

 exterior surface always covered by a thin, elastic, horny epi- 

 dermis. 



1. Balanus balanoides, pi. LIII, f. 17, and pi. LIV, f. 

 4,5. 



Balanus ovularis, First Ed., pi. 6, f. 4, 5, and pi. 7, f. 17 ; 

 Lamarck, V, p. 392; Balanus balanoides, Montagu, p. 7; Lepas 

 balanoides, Donovan, pi. 36, f. 2 ; Maton and Rackett, p. 23 ; 

 Brown, Ency. Brit., VI, p. 402. 



Shell subconic, subdepressed ; valves smooth, white, some- 

 times deeply sulcated at the base ; aperture wide ; operculum 

 with the two anterior valves slightly striated transversely, the 

 posterior ones smooth. 



Fig. 8, 9, valves of the operculum. 



Fig. 5, an elongated variety. 



A very common species, adhering to muscles and oysters. 



2. Balanus communis, pi. LIII, f. 23, and pi. LIV, f. 1. 

 Balanus communis, First Ed., pi. 6, f. 1 , and pi. 7, f. 23 ; 



Montagu, p. 6 ; Lepas Balanus, Pennant, IV, p. 72, pi. 37, f. 

 4 ; Donovan, I, pi. 30, f. 1 ; Maton and Rackett, p. 23 ; Fle- 

 ming, Edin. Ency., Art. Conch., p. 102. 



Shell strong, rugged, conic, compartments unequal, with 

 many irregular, longitudinal, squammose ribs ; the interstices 

 with transverse wrinkles ; aperture rather contracted, and fur- 

 nished with a four-valved operculum; posterior valves spreading 

 a little at the apex ; anterior valves transversely striated, and 

 provided with a longitudinal furrow ; colour cinereous-brown. 



Common on most of the coasts of Britain and Ireland, ad- 

 hering to extraneous substances. 



3. Balanus rugosus, pi. LIII, f. 4, 7, 8, and 21, and pi. 

 LIV, f. 6. 



Balanus rugosus, First Ed., pi. 6, f. 6, and pi. 7, f. 4 and 20 ; 

 Montagu, p. 8; Fleming, Edin. Ency., Art. Conch., p. 101; 

 Maton and Rackett, p. 25; Lepas borealis, Donovan, pi. 160, 

 lower figure. 



Shell subconic, divided into six compartments by irregular, 

 inequidistant furrows, those of the posterior side broadest, and 

 crossed with deep divisions, formed by the lines of growth, 

 these are sometimes wrinkled or striated longitudinally ; aper- 

 ture very large, inner margin transversely ridged, and closed 

 by a four-valved operculum; the dorsal valves a little apart and 

 reflexed at the apex ; upper half of anterior valves smooth, 

 with transverse, strong stria; on their lower half; colour cream- 

 white. 



Fig. 21, an elongated variety, the B.Jistulusus of authors. 



Fig. 13, 14, the operculum. 



Common on many of the British and Irish coasts. 



4. Balanus costatus, pi. LIV, f. 2, 3. 



Balanus costatus, First Ed., pi. 6, f. 2, 3 ; Montagu, p. 1 1 ; 

 Fleming, Edin. Ency., Art. Conch., p. 101 ; Lepas costata, 

 Donovan, 1, pi. 30, f. 2 ; Maton and Rackett, p. 24. 



